JP2013247352A - Composite magnetic material, its manufacturing method, antenna, and communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide composite magnetic material that is applicable to a frequency band from 70 MHz to 500 MHz and the real part μr' of its complex magnetic permeability in the frequency band becomes larger, and its manufacturing method, an antenna, and a communication device.SOLUTION: Composite magnetic material according to the invention is composite magnetic material formed by distributing magnetic powder in insulation material. For the magnetic powder, its average thickness is 0.01 μm or more and 10 μm or less, its average major axis is 0.05 μm or more and 20 μm or less, its average aspect ratio (major axis/thickness) is 5 or more with flat shape, and the real part μr' of its complex magnetic permeability in a frequency band from 70 MHz to 500 MHz is 7 or more.

Description

  The present invention relates to a composite magnetic body, a method for manufacturing the same, an antenna, and a communication device, and more particularly, a composite magnetic body suitable for use as a material for loading an antenna or an electronic component using an electromagnetic wave in a frequency band from 70 MHz to 500 MHz. And a manufacturing method thereof, an antenna including the composite magnetic body, and a communication device such as a portable telephone and a portable information terminal including the antenna.

As information communication devices increase in speed and density, there is a strong demand for miniaturization of antennas and electronic components mounted on electronic devices. In general, the wavelength λg of an electromagnetic wave propagating in a substance is defined by the wavelength λo of the electromagnetic wave propagating in a vacuum, the real part εr ′ (hereinafter sometimes abbreviated as εr ′) of the complex permittivity of the substance, and the complex permeability. Using the real part μr ′ (hereinafter sometimes abbreviated as μr ′),
λg = λo / (εr ′ · μr ′) ^1/2 (1)
It can be expressed as. According to this equation (1), it is known that the larger the εr ′ and μr ′ are, the larger the shortening rate of the wavelength λg is, so that the antenna and electronic components can be miniaturized.

Further, the characteristic impedance Z _g of material with a characteristic impedance Z ₀ of the vacuum,
Z _g = Z ₀ · (μr ′ / εr ′) ^1/2 (2)
It can be expressed as. According to this equation (2), the smaller the difference between the values of .epsilon.r 'and .mu.r', the characteristic impedance Z ₀ of the vacuum, becomes smaller difference between the value of the characteristic impedance Z _g of the composite magnetic body. On the other hand, the characteristic impedance of the space in which the electromagnetic wave flies is almost the same value as the vacuum characteristic impedance Z ₀ , so that the smaller the difference between the values of εr ′ and μr ′, the lower the power loss for impedance matching.
Further, when the wavelength of the electromagnetic wave is shortened according to the equation (1), the values of εr ′ and μr ′ may be increased, but the frequency at which transmission and reception can be performed when the difference between the value of εr ′ and the value of μr ′ is large. It is also known that the bandwidth is narrowed. Therefore, it is known that the difference between the value of εr ′ and the value of μr ′ needs to be small in order to transmit and receive a large amount of information in a wide frequency band.

  By the way, in the VHF band of 90 to 220 MHz in recent years, from the viewpoint of effective use of radio resources, a change from the use for analog television to another use is planned. Among these applications, portable information terminals are particularly promising. However, in this portable information terminal, it is difficult to reduce the size of the antenna due to the long wavelength of the radio wave in the VHF band. An antenna or an earphone cord must be used as an antenna.

On the other hand, since the use of portable information terminals has expanded from calls to communications other than calls, the portable information terminals can be received even when they are placed in bags or pockets. Built into the terminal is a must. Therefore, there is a demand for a magnetic material that has a large wavelength shortening effect and can reduce the size of the VHF band antenna.
However, when a conventional magnetic material is applied to a VHF band antenna, an eddy current is generated on the surface of the magnetic material, and the magnetic material has a magnetic permeability in order to generate a magnetic field in a direction that cancels the change in the applied magnetic field. There was a problem that apparently decreased.
Further, since an increase in eddy current causes energy loss due to Joule heat, it is difficult to use a magnetic material as a material for an antenna, an electronic component or the like.

Therefore, the present inventors are a composite in which spherical or flat magnetic powder is dispersed in an insulating material, the real part μr ′ of the complex permeability at 1 GHz is larger than 1, and the complex permeability is A composite magnetic body having a loss tangent tan δμ of 0.1 or less has been proposed (Patent Document 1).
According to this composite magnetic body, it is possible to avoid deterioration of magnetic characteristics due to eddy current, and it is possible to reduce magnetic loss even in a frequency band of 500 MHz to 1 GHz.
On the other hand, high frequency ferrites have been proposed as magnetic materials that can be used in the VHF band.

JP 2008-181905 A

  However, in the composite magnetic material proposed by the present inventors, the magnetic characteristics are deteriorated due to eddy current and the loss tangent tan δμ (hereinafter sometimes abbreviated as tan δμ) of the complex permeability in the frequency band of 500 MHz to 1 GHz is reduced. However, at a frequency lower than 500 MHz, the loss tangent tan δμ of the complex permeability tends to increase. In particular, the loss tangent at 100 MHz exceeds 0.1. Therefore, even if this composite magnetic material is applied to a VHF band antenna, there is a problem that it is difficult to further downsize the antenna.

In addition, although the high frequency ferrite can be used in the VHF band, the VHF band is a frequency band in which the influence of resonance loss is noticeable, so that the frequency dependence of μr ′ is large and the circuit design is difficult. There was a point.
Furthermore, since ferrite is a ceramic, there is a problem that shape workability and mechanical reliability are poor, and therefore, when applied to a portable information terminal, various limitations occur, which is not preferable.

  The present invention has been made in view of the above circumstances, and is applicable to a frequency band from 70 MHz to 500 MHz, and in addition, a composite magnetism that increases the real part μr ′ of the complex permeability in this frequency band. It is an object to provide a body, a manufacturing method thereof, an antenna, and a communication device.

  As a result of intensive studies to solve the above problems, the present inventors have made the shape of the magnetic powder flat in a composite magnetic body in which magnetic powder is dispersed in an insulating material. If the real part μr ′ of the complex permeability in the frequency band from 70 MHz to 500 MHz is set to 7 or more, this composite magnetic body can be applied to the VHF band antenna. The inventors have found that it is possible to incorporate an antenna into a portable information terminal, and have completed the present invention.

  That is, the composite magnetic body of the present invention is a composite magnetic body in which magnetic powder is dispersed in an insulating material. The magnetic powder is flat and has a complex permeability in a frequency band from 70 MHz to 500 MHz. The part μr ′ is 7 or more.

In the composite magnetic body of the present invention, the loss tangent tan δμ of the complex permeability in the frequency band from 70 MHz to 220 MHz is preferably 0.1 or less.
The porosity is preferably 20% or less.
The real part εr ′ of the complex dielectric constant in the frequency band from 70 MHz to 500 MHz is preferably 15 or more, and the loss tangent tan δε of the complex dielectric constant is preferably 0.1 or less.
The magnetic powder preferably has an average thickness of 0.01 μm or more and 10 μm or less, an average major axis of 0.05 μm or more and 20 μm or less, and an average aspect ratio (major axis / thickness) of 5 or more.

  In the method for producing a composite magnetic body of the present invention, a slurry and a dispersion medium in which spherical magnetic particles having an average particle diameter of 3 μm or less are dispersed in a solution, and the slurry and the dispersion medium are sealed in a sealable container. Filled so that the total volume is the same as the volume in the container, the slurry is stirred together with the dispersion medium in a sealed state, and the spherical magnetic particles are deformed and fused together to form a flat magnetic powder. A first step in which the flat magnetic powder is mixed with an insulating material to form a molding material, and the molding material is molded or applied onto a substrate, dried, heat-treated or And a third step of firing.

  The antenna of the present invention is loaded with the composite magnetic material of the present invention, and is characterized by transmitting, receiving or transmitting / receiving electromagnetic waves in a frequency band from 70 MHz to 500 MHz.

  A communication apparatus according to the present invention includes the antenna according to the present invention.

According to the composite magnetic body of the present invention, the magnetic powder is flattened, and the real part μr ′ of the complex permeability in the frequency band from 70 MHz to 500 MHz is set to 7 or more. There is almost no reduction in wavelength in this frequency band.
Therefore, if this composite magnetic body is applied to a VHF band antenna, generation of eddy currents on the surface of the composite magnetic body can be prevented, μr ′ can be prevented from being lowered, and the antenna can be further reduced in size. Can be achieved.
Therefore, if this composite magnetic body is applied to a VHF band antenna or electronic component, the antenna or electronic component can be further reduced in size.

  According to the method for producing a composite magnetic body of the present invention, a slurry and a dispersion medium in which spherical magnetic particles having an average particle diameter of 3 μm or less are dispersed in a solution, the slurry and the dispersion are contained in a sealable container. Filled so that the total volume of the medium is the same as the volume in the container, the slurry is stirred together with the dispersion medium in a sealed state, and the spherical magnetic particles are deformed and fused together to form a flat shape. A first step of forming magnetic powder, a second step of mixing the flat magnetic powder with an insulating material to form a molding material, and molding or applying the molding material on a substrate and drying. And a third step of heat treatment or firing, and therefore, a composite magnetic body having μr ′ of 7 or more in a frequency band from 70 MHz to 500 MHz can be easily produced.

  According to the antenna of the present invention, the composite magnetic body of the present invention is loaded, and electromagnetic waves in the frequency band from 70 MHz to 500 MHz are transmitted, received, or transmitted / received. Therefore, electromagnetic waves in the frequency band from 70 MHz to 500 MHz are used. The reliability of transmission, reception or transmission / reception can be improved.

According to the communication device of the present invention, since the antenna of the present invention is provided, the reliability of transmission, reception or transmission / reception of electromagnetic waves in the frequency band from 70 MHz to 500 MHz can be improved.
Further, by using a miniaturized antenna, the entire communication device can be miniaturized. Therefore, a further miniaturized communication apparatus can be provided.

It is a figure which shows a mode that the slurry containing a spherical magnetic particle and dispersion medium are stirred at high speed using an open container. It is a figure which shows a mode that the slurry and dispersion medium containing a spherical magnetic particle are stirred at high speed using an airtight container. It is a schematic diagram which shows the electric power feeding method of the monopole antenna which is an example of the antenna of one Embodiment of this invention. It is a perspective view which shows an example of the kind of portable telephone of the communication apparatus of one Embodiment of this invention. It is a perspective view which shows another example of a kind of portable telephone of the communication apparatus of one Embodiment of this invention. It is a perspective view which shows another example of a kind of portable telephone of the communication apparatus of one Embodiment of this invention. It is a perspective view which shows another example of a kind of portable telephone of the communication apparatus of one Embodiment of this invention. It is a figure which shows the complex magnetic permeability and loss tangent of the composite magnetic body of Example 1 of this invention. It is a scanning electron microscope (SEM) image which shows the structure of the composite magnetic body of Example 1 of this invention. It is a figure which shows the complex magnetic permeability and loss tangent of the composite magnetic body of Example 2 of this invention. It is a figure which shows the complex magnetic permeability and loss tangent of the composite magnetic body of the comparative example 1. 3 is a scanning electron microscope (SEM) image showing the structure of the composite magnetic body of Comparative Example 1.

The composite magnetic body according to the present invention, a manufacturing method thereof, an antenna, and a mode for carrying out a communication device will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[Composite magnetic material]
The composite magnetic body of the present embodiment is a composite magnetic body in which magnetic powder is dispersed in an insulating material. This magnetic powder is flat, and the real part of the complex permeability in the frequency band from 70 MHz to 500 MHz. It is a composite magnetic material having μr ′ of 7 or more.
In the composite magnetic body of this embodiment, the loss tangent tan δμ of the complex permeability in the frequency band from 70 MHz to 220 MHz is preferably 0.1 or less, more preferably 0.05 or less, and More preferably, it is 04 or less.

  Here, the reason why the real permeability μr ′ of the complex permeability and the loss tangent tan δμ of the complex permeability are preferable in the above range is that this range can reduce the wavelength of the electromagnetic wave and the magnetic loss due to the eddy current. This is because the energy loss is reduced and the energy loss is reduced.

The magnitude of this energy loss can be expressed by an imaginary part μr ″ (hereinafter sometimes abbreviated as μr ″) of the complex permeability shown in the following formula (3).
μr ″ = μr ′ × tan δμ (3)
Here, since the imaginary part μr ″ of the complex permeability is preferably 0.5 or less, from the above equation (3), when μr ′ is 10, tan δμ is 0.05 or less. Further, when μr ′ is 15, tan δμ is preferably 1/30 or less.

In this composite magnetic body, the porosity is preferably 20% or less.
Here, the porosity of the composite magnetic body can be obtained by the following equation (4).
Porosity = (1−Measured density / Theoretical density) × 100 (4)
The theoretical density of the composite magnetic body is calculated in consideration of the mixing ratio of the magnetic powder and the insulating material based on the theoretical density of the magnetic powder and the theoretical density of the insulating material (≈measured density).
As a method of calculating the theoretical density of the magnetic powder, there is a method of calculating a lattice constant from an X-ray diffraction pattern of the magnetic powder and calculating a theoretical density value based on the lattice constant and the crystal structure.

On the other hand, as a method for calculating the measured density of the insulating material, for example, when the insulating material is resin, only the resin is cured and the outer dimensions and mass are measured, and the measured density is calculated from these measured values. There is.
In addition, as a method for calculating the actual density of the composite magnetic body, for example, there are a method of measuring the external dimensions and mass, a method of calculating the actual density from these measured values, and a method of using a value measured by the pycnometer method.

In this composite magnetic body, more preferably, the real part μr ′ of the complex permeability in the frequency band from 70 MHz to 500 MHz is 7 or more, the real part εr ′ of the complex permittivity is 15 or more, and the loss tangent tan δμ of the complex permeability is The loss tangent tan δε of the complex dielectric constant is 0.05 or less and 0.1 or less.
In particular, the real part μr ′ of the complex permeability in the frequency band from 90 MHz to 220 MHz is preferably 7 or more and the loss tangent tan δμ of the complex permittivity is 0.05 or less.

In this composite magnetic body, the real part μr ′ of the complex permeability is 7 or more, the real part εr ′ of the complex permittivity is 15 or more, and (μr ′ · εr ′) ^−1/2 is 0.1 or less. , (Μr ′ / εr ′) ^1/2 is preferably 0.5 or more and 1 or less.
Further, it is preferable that the loss tangent tan δμ of the complex permeability is 0.05 or less and the loss tangent tan δε of the complex dielectric constant is 0.1 or less.

In the composite magnetic body of the present embodiment, the real part μr ′ of the complex permeability in the frequency band of 70 MHz or more and 500 MHz or less is 7 or more, the real part εr ′ of the complex permittivity is 15 or more, and (μr ′ · [epsilon] r ') ^-1/2 is preferably 0.1 or less, and ([mu] r' / [epsilon] r ') ^1/2 is preferably 0.5 or more and 1 or less.
Further, it is preferable that the loss tangent tan δμ of the complex permeability is 0.05 or less and the loss tangent tan δε of the complex dielectric constant is 0.1 or less.
The real part μr ′ of the complex permeability, the real part εr ′ of the complex permittivity, the loss tangent tan δμ of the complex permeability and the loss tangent tan δ∈ of the complex permittivity are values measured by a material analyzer. The device is not limited to a material analyzer as long as the above values can be measured with the same accuracy as a material analyzer.

In this composite magnetic body, the real part μr ′ of the complex permeability, the real part εr ′ of the complex permittivity, (μr ′ · εr ′) − ^1/2 and (μr ′ / εr ′) ^1/2 The reason why the above range is preferable as a value will be described in detail by taking the case where this composite magnetic body is loaded on an antenna as an example.
The same effect can be obtained with all electronic components using high frequencies other than the antenna.

First, the real part μr ′ of the complex permeability is preferably 7 or more, more preferably 9 or more. Here, the reason why μr ′ is set to 7 or more is that the real part εr ′ of the complex dielectric constant usually shows a large value of 15 or more. Therefore, when μr ′ is set to less than 7, μr ′ is smaller than εr ′. This is because the power loss due to the mismatch of the characteristic impedance is increased.
The upper limit of μr ′ is not particularly limited, but is preferably 30 or less, more preferably 20 or less, from the aspect ratio and content ratio of the magnetic powder that can be actually produced.

  The real part εr ′ of the complex dielectric constant is preferably 15 or more, more preferably 20 or more. Here, the reason why εr ′ is set to 15 or more is that it is an effective value for achieving miniaturization of the antenna according to the above equation (1). In consideration of the upper limit of εr ′, 30 or less is preferable.

In this composite magnetic body, it is preferable that (μr ′ · εr ′) ^−1/2 is 0.1 or less when the values of μr ′ and εr ′ are in the above ranges. The reason is as follows.
The value of (μr ′ · εr ′) ^−1/2 is a shortening rate of the high frequency wavelength in the composite magnetic material with respect to the wavelength in vacuum, as shown in the equation (1). In addition, the wavelength in vacuum and the wavelength in normal air show a substantially equal value.

  In general, an antenna is usually constituted by an antenna conductor made of a conducting wire having a length of ½ or ¼ of a wavelength. In the long wavelength region where the frequency is low, particularly in the frequency band of 70 MHz to 500 MHz, the wavelength is 60 cm or more, and the length of the antenna conductor is 30 cm or more or 15 cm or more, and the antenna itself becomes large. Therefore, when a long-wavelength signal is matched with an electronic circuit using a matching circuit for transmission and reception, and the antenna length is shortened, the amount of current on the antenna conductor is reduced. Problems such as narrowing and reduced radiation efficiency occur. In particular, when the length of the antenna is set to 1/10 or less of the wavelength, transmission / reception of radio waves becomes difficult, which is a practical problem.

Therefore, if a composite magnetic material having (μr ′ · εr ′) ^−1/2 of 0.1 or less is loaded on the antenna, the high frequency wavelength is theoretically reduced to approximately 1/10 or less on the composite magnetic material. Is done. Therefore, the size of the antenna can be reduced without narrowing the band or reducing the radiation efficiency as in the case of using the matching circuit.

The above (μr ′ / εr ′) ^1/2 is preferably 0.5 or more and 1 or less. The reason is as follows.
The value of (μr ′ / εr ′) ^1/2 is the ratio (Z _g / Z _{0 )} between the characteristic impedance Z _g of the composite magnetic material and the characteristic impedance Z _{0 of the} vacuum as shown in the above formula (2). Therefore, the characteristic impedance Z _g of the composite magnetic material is (μr ′ / εr ′) ^½ times the vacuum characteristic impedance Z ₀ . Here, it is assumed that the characteristic impedance of the vacuum and the characteristic impedance of the normal atmosphere are substantially equal.

Usually, μr ′ of the composite magnetic body is smaller than εr ′, and therefore the characteristic impedance Z _g of the composite magnetic body is smaller than the value of the atmospheric characteristic impedance Z _A (≈vacuum characteristic impedance Z ₀ ). It is known that a high-frequency signal is attenuated by reflection or absorption when propagating from a region having a large characteristic impedance to a region having a small characteristic impedance.

Therefore, when the characteristic impedance Z _g of the composite magnetic body also reduced 50% or more than the characteristic impedance Z _A of the atmosphere, high frequency attenuation rate becomes extremely large, and practical problems. Therefore, when the value of (μr ′ / εr ′) ^1/2 is 0.5 or more, the change in characteristic impedance can be suppressed to 50% or less when electromagnetic waves propagate from the atmosphere to the composite magnetic body. Therefore, the attenuation of the high frequency signal can be suppressed. Further, the characteristic impedance Z _g of the composite magnetic body, if greater than the impedance Z _A of the atmosphere, the electromagnetic wave difference even slight these characteristic impedances is greatly attenuated. Therefore, the value of (μr ′ / εr ′) ^1/2 is preferably 1 or less.

The complex magnetic material has a complex magnetic loss loss tangent tan δμ of preferably 0.1 or less, more preferably 0.05 or less, and still more preferably 0.04 or less. Further, the loss tangent tan δε (hereinafter sometimes simply referred to as tan δε) of the complex dielectric constant of the composite magnetic material is preferably 0.1 or less, and more preferably 0.07 or less.
The tan δμ of this composite magnetic material from 70 MHz to 500 MHz, more preferably from 90 MHz to 220 MHz is preferably 0.1 or less, more preferably 0.05 or less, even more preferably 0.04 or less. The tan δε of the body is preferably 0.1 or less, more preferably 0.07 or less.
Here, the reason why μr ′, tan δμ, εr ′, and tan δε are preferably in the above ranges is that this range can shorten the wavelength of the electromagnetic wave, reduce magnetic loss due to eddy current, etc., and reduce energy loss. This is because the range in which becomes smaller.

  As described above, when the values of tan δμ and tan δε exceed preferable values, the high frequency corresponds to the imaginary part μr ″ of the complex permeability or the imaginary part εr ″ of the complex permittivity in the composite magnetic body. Since only the portion is absorbed and changed to heat, the energy of the high-frequency signal is attenuated, and there is a possibility that problems such as a decrease in S / N ratio and heat generation may occur.

In the composite magnetic body of this embodiment, if various characteristics such as the real part μr ′ of the complex permeability in the frequency band from 70 MHz to 500 MHz satisfy the above range, the frequency ranges from 70 MHz to 500 MHz, preferably from 90 MHz to 220 MHz. Even in electronic devices and electronic devices used in frequency bands, for example, antennas for communication devices such as mobile phones, personal digital assistants, and multifunctional mobile information devices, both miniaturization and reduction of power loss can be achieved. it can.
Furthermore, in the case of a frequency band of 500 MHz or less, preferably 220 MHz or less, tan δμ and tan δε are lower than in the case of a frequency band exceeding 500 MHz, which is preferable because the gain of the antenna is increased.

When the porosity in the composite magnetic material is 20% or less, μr ′ of the composite magnetic material is improved, but εr ′ is hardly changed. As a result, the antenna of a communication device such as an electronic component or an electronic device to which the composite magnetic body is applied, for example, a portable telephone, a portable information terminal, or a multifunctional portable information device can be reduced in size, and power loss can be reduced. It is preferable because it can be considered that it can be suppressed.
The mechanism for obtaining such an effect is considered as follows.

When the porosity in the composite magnetic body increases, the amount of magnetic powder per unit volume of the composite magnetic body decreases, so μr ′ decreases. On the other hand, since the surface of the pores has a capacitance at the interface with the magnetic powder in the same manner as the insulating material, the value of εr ′ hardly changes even when the porosity is increased.
Further, when the porosity in the composite magnetic body decreases, the amount of magnetic powder per unit volume of the composite magnetic body increases, so μr ′ increases. On the other hand, as described above, since the value of εr ′ is hardly affected by the porosity, the value of εr ′ is almost the same value.

  That is, by decreasing the porosity in the composite magnetic material, the value of μr ′ increases, but the value of εr ′ hardly changes, so the difference between the value of μr ′ and the value of εr ′ decreases. Therefore, by setting the porosity of a composite magnetic body in which a magnetic powder having an average aspect ratio (major axis / thickness) of 5 or more is dispersed in an insulating material to 20% or less, an electronic component including the composite magnetic body, The electronic device can be reduced in size, and power loss due to impedance matching can be suppressed.

  The method for reducing the porosity of the composite magnetic material is not particularly limited as long as it is a method capable of reducing the porosity of the composite magnetic material to 20% or less. For example, a method for preventing the aggregation of magnetic powders by improving the dispersibility of magnetic powders in insulating materials, a method for improving the curability of insulating materials by optimizing the type and amount of hardener, and fluidity Select a high-insulating material, make the insulating material easy to enter the gap between the magnetic powder, a method to reduce the internal pores by pressurizing the obtained composite magnetic body, etc. Includes a method combining these methods.

Here, the magnetic powder and the insulating material constituting the composite magnetic body of the present embodiment will be described in detail.
"Magnetic powder"
The reason why the shape of the magnetic powder is preferably flat is as follows.
The magnitude of the demagnetizing field in the magnetic powder depends on the shape of the powder. For example, when the magnetic powder is spherical, since the demagnetizing field is isotropic, the magnetic permeability obtained is isotropic, and it is difficult to obtain excellent magnetic properties in the high frequency region. On the other hand, when the magnetic powder is flat, the demagnetizing field in the direction parallel to the flat surface is remarkably reduced, and thus the obtained μr ′ is increased.

  The magnetic powder of the present embodiment is formed into a flat shape by deforming and fusing the spherical magnetic particles by applying mechanical stress to the spherical magnetic particles having an average particle diameter of 10 nm or more and 3 μm or less. preferable.

  The average aspect ratio (major diameter (maximum length in the particle) / thickness) of the magnetic powder is such that the major diameter and thickness of each of the plurality of magnetic powders, for example, 100 or more magnetic powders, preferably 500 By measuring the major axis and thickness of each magnetic powder, the aspect ratio (major axis / thickness) of each individual magnetic powder is determined, and the average value of these aspect ratios (major axis / thickness) is calculated. .

The average aspect ratio (major axis / thickness) thus obtained is preferably 5 or more, more preferably 7 or more.
Here, when the average aspect ratio (major axis / thickness) of the magnetic powder is less than 5, the demagnetizing field coefficient due to the particle shape increases, and accordingly, the effective magnetic field applied when the composite magnetic body is produced decreases. Μr ′ of the obtained composite magnetic body becomes small, and as a result, it is not possible to obtain sufficient μr ′ for downsizing electronic components and electronic devices.

On the other hand, when the average aspect ratio increases, the mechanical strength of the magnetic powder itself may be reduced. Therefore, in order to ensure the desired mechanical strength of the magnetic powder, the average aspect ratio is preferably 15 or less, and practically about 20 is the upper limit.
Furthermore, when the average aspect ratio exceeds 20, the shape of the magnetic powder is too flat, the space between the magnetic particles is narrowed, and a space in which the insulating material does not easily enter is easily formed therebetween, as a result, Bubbles are likely to be generated in the composite magnetic material, and the presence of the bubbles lowers μr ′, which is not preferable.
Considering the above points, the average aspect ratio of the magnetic powder is preferably 5 or more and 20 or less, and more preferably 7 or more and 15 or less.

  Similarly to the average aspect ratio (major axis / thickness), the average thickness and the major axis of the magnetic powder are also the thickness and major axis of each of the plurality of magnetic powders, for example, 100 or more magnetic powders, preferably 500. It can be obtained by measuring the thickness and major axis of each of the magnetic powders and calculating the average value of the thickness and major axis.

The average thickness of the magnetic powder is preferably 0.1 μm or more and 10 μm or less, more preferably 0.1 μm or more and 1 μm or less.
In particular, when this magnetic powder is used in a high frequency band of 70 MHz or more, a preferable range of the average thickness is 0.1 μm or more and 0.5 μm or less.
Here, when the average thickness of the magnetic powder is less than 0.1 μm, it is difficult to manufacture the magnetic powder itself, and it is difficult to handle the composite magnetic body. As a result, the orientation is good and the μr ′ is high. Since it becomes difficult to obtain a composite magnetic body, it is not preferable. On the other hand, if the average thickness of the magnetic powder exceeds 10 μm, an eddy current or the like is generated when a high frequency is applied, and μr ′ of the obtained composite magnetic material is lowered, which is not preferable.

The average major axis of the magnetic powder is preferably 0.05 μm or more and 20 μm or less, and more preferably 0.2 μm or more and 10 μm or less.
Here, if the average major axis of the magnetic powder is less than 0.05 μm, it is difficult to manufacture the magnetic powder itself, and it is difficult to handle the composite magnetic body. As a result, the orientation is good and the complex permeability is low. This is not preferable because it is difficult to obtain a composite magnetic body having a high real part μr ′.
Thus, by setting the average thickness, average major axis, and aspect ratio of the magnetic powder within the above ranges, μr ′ exhibits a substantially constant value in the frequency band from 70 MHz to 500 MHz.

The material constituting the magnetic powder is not particularly limited as long as it is a magnetic material. For example, nickel (Ni), iron (Fe), cobalt (Co), gadolinium (Gd), terbium (Tb) ), A ferromagnetic metal such as dysprosium (Dy), a metal composed of any one of paramagnetic metals such as molybdenum (Mo), or an alloy containing at least one of these metals.
These metals or alloys may contain diamagnetic metals such as copper (Cu), zinc (Zn), and bismuth (Bi).

Examples of these alloys include two-element alloys and three-element alloys.
Examples of the two-element alloys include Fe-Ni alloys such as Permalloy (registered trademark) exhibiting soft magnetism with a coercive force of 70 Oersted (Oe) or less, Fe-Si alloys, Fe-Co alloys, Fe-Cr alloys, and the like. It is done.
Examples of the ternary alloy include Fe—Ni—Mo alloys such as Supermalloy (registered trademark), Fe—Si—Al alloys such as Sendust (registered trademark), Fe—Cr—Si alloys, and the like.
Among these alloys, as an Fe—Ni alloy, an alloy of Ni 78% by mass—Fe 22% by mass can be easily obtained with an average thickness of magnetic powder of 0.5 μm or less and an average major axis of 10 μm or less. A composite magnetic body having a low magnetic loss as well as a magnetic constant can be obtained, which is preferable.

  A metal element that is not included in the alloy and has similar properties to the alloy (a metal that is close to the metal in the alloy in the periodic table), such as aluminum (Al), chromium (Cr), manganese (Mn), cobalt (Co), copper (Cu), zinc (Zn), niobium (Nb), molybdenum (Mo), indium (In), tin (Sn), etc. Two or more kinds may be appropriately selected and added.

When the above metal element is added to the alloy, the content of the metal element is preferably 0.1% by mass or more and 90% by mass or less, preferably 1% by mass with respect to the total mass of the metal element and the alloy. It is more preferably 12% by mass or less, and further preferably 1% by mass or more and 5% by mass or less.
Here, the reason why the metal element content is limited to the above range is that, if the metal element content is less than 0.1% by mass, sufficient plasticity for flattening the spherical magnetic particles described later is used. On the other hand, when the content exceeds 90% by mass, the magnetic moment of the metal element itself is small, so that the saturation magnetization of the entire magnetic powder becomes small, and as a result, obtained. This is because μr ′ is also reduced.

  Particularly, a group of soft metals such as aluminum (Al), zinc (Zn), indium (In), and tin (Sn) in that the aspect ratio is high and a high μr ′ composite magnetic body is easily obtained as a result. It is preferable to use an iron-nickel alloy containing one or more metal elements selected from 1 to 12% by mass, preferably 1 to 5% by mass.

  Among these, the nickel-iron-zinc (Ni-Fe-Zn) alloy has a large aspect ratio because the workability of spherical magnetic particles described later is enhanced by the addition of Zn to the Fe-Ni alloy. This is preferable because magnetic powder can be easily obtained. As the composition ratio of the alloys, for example, alloys of Ni 75% by mass—Fe 20% by mass—Zn 5% by mass, Ni 76% by mass—Fe 20% by mass—Zn 4% by mass, and the like can be suitably used.

  This magnetic powder is preferably an insulating magnetic powder. By using the insulating magnetic powder, it is possible to suppress the formation of a conductive path due to the contact between the magnetic powders in the composite magnetic material. As a result, the dielectric loss of the composite magnetic material can be reduced. Can be reduced. In this insulating magnetic powder, it is sufficient that at least the surface of the particles has an insulating property.

The method for making the magnetic powder insulative is not particularly limited, and examples thereof include a method of forming an insulating oxide film of about 5 nm on the surface of the magnetic powder.
Normally, when the magnetic powder is handled in the air, an oxide film is naturally formed on the surface of the magnetic powder, but the oxide film formed naturally has insufficient insulation, It is difficult to reduce dielectric loss. Therefore, in order to reduce the dielectric loss of the composite magnetic material, the surface of the magnetic powder is insulated by about 5 nm by heat treatment at a temperature of 50 ° C. or more and 200 ° C. or less for about 1 hour to several hours. It is preferable to form an oxide film.

  Further, an insulating film having a composition different from that of the magnetic powder may be formed on the surface of the magnetic powder. Examples of such a composition include inorganic substances such as silicon oxide and phosphate, or organic substances such as resins and surfactants. These insulating films may be formed on the surface of a magnetic powder having an oxide film (including an oxide film formed by natural oxidation or heat oxidation), or may be formed on the surface of a magnetic powder having no oxide film. Good.

"Insulating material"
The insulating material is not particularly limited as long as it is an insulating material. However, when the composite magnetic body of the present embodiment is used as an antenna for a mobile phone or an antenna for a portable information terminal, the mechanical strength is high and the hygroscopic property is high. It is preferable that it is low and it is excellent in shape workability. Examples of such insulating materials include polyamide resins, polyimide resins, polyamideimide resins, polyetherimide resins, polycarbonate resins, polyacetal resins, polybutylene terephthalate resins, polybenzoxazole resins, polyphenylene resins, polybenzocyclobutene resins, Polyarylene ether resin, polysiloxane resin, epoxy resin, polyester resin, fluorine resin, polyolefin resin, polycycloolefin resin, cyanate resin, polyphenylene ether resin, polyphenylene sulfide resin, polyarylate resin, polyether ether ketone resin, polysulfone resin, Thermosetting resin or thermoplastic resin such as polyethersulfone resin, norbornene resin, ABS resin, polystyrene resin, etc. is preferably used It is. These resins may be used alone or in combination of two or more.

  Among epoxy resins, resins having a cyclic structure in the main chain, in particular an alicyclic ring structure, and a functional group that polymerizes in monomer units are difficult to get entangled with the magnetic powder. This is preferable because there is no risk of inhibition and a high μr ′ is easily obtained. An example of such a resin is a dicyclopentadiene type resin.

  When using a hard resin such as this dicyclopentadiene type resin, in order to reduce the porosity of the composite magnetic body and to improve the handleability in production, such a hard resin is stretched to the composite magnetic body. Alternatively, an insulating resin imparting flexibility may be mixed. The insulating resin that imparts stretchability and flexibility may be appropriately selected from the above-described resins, and liquid epoxy resins and bisphenol type epoxy resins are particularly preferable.

When this dicyclopentadiene type resin or the like is used in combination with the above liquid epoxy resin or bisphenol type epoxy resin, the content of the dicyclopentadiene type resin or the like with respect to the total amount of the resin is 50% by mass or more and 90% by mass or less. It is preferable that By setting the content of the dicyclopentadiene type resin or the like in the above range, the orientation of the magnetic powder can be improved and high μr ′ can be obtained.
Furthermore, since the insulating resin imparting stretchability and flexibility is contained in an amount of 10% by mass or more and 50% by mass or less, the resin can easily enter the gaps between the magnetic powders, thereby generating pores in the composite magnetic body. It is preferable because it can be suppressed and the porosity can be reduced.

Further, a thermoplastic elastomer may be added in addition to the insulating material. By adding this thermoplastic elastomer, the mechanical strength and shape processability of the composite magnetic material can be improved. Therefore, the composite magnetic body to which this thermoplastic elastomer is added is excellent in toughness, flexibility and deformability.
As the thermoplastic elastomer, one or more selected from the group of styrene elastomer, olefin elastomer, vinyl chloride elastomer, urethane elastomer, ester elastomer and amide elastomer can be used.
The amount of the thermoplastic elastomer added may be adjusted as appropriate in consideration of the heat resistance required for the application of the composite magnetic material.

[Production Method of Composite Magnetic Material]
In the method of manufacturing a composite magnetic body according to the present embodiment, a slurry and a dispersion medium obtained by dispersing spherical magnetic particles having an average particle diameter of 3 μm or less in a solution are placed in a sealable container. And the slurry is stirred together with the dispersion medium in a sealed state, and the spherical magnetic particles are deformed and fused together to form a flat magnet. A first step of forming powder, a second step of mixing the flat magnetic powder with an insulating material to form a molding material, molding or applying the molding material on a substrate, and drying, And a third step of heat treatment or baking.

Hereinafter, each step will be described in detail.
(First step)
First, spherical magnetic particles having an average particle diameter of 10 nm or more and 3 μm or less are dispersed in a solution containing a surfactant to obtain a slurry.
The composition of the magnetic particles is exactly the same as the composition of the above magnetic powder.
As the surfactant, a surfactant containing an element such as nitrogen, phosphorus or sulfur that is compatible with the surface of the magnetic particles is preferable. For example, a nitrogen-containing block copolymer, phosphate, polyvinylpyrrolidone, or the like is added. preferable.

  As the solvent, an organic solvent is preferable because it is necessary to prevent oxidation of the metal element contained in the magnetic particles, and a nonpolar organic solvent such as xylene, toluene, cyclopentanone, cyclohexanone is particularly preferable.

  Next, the slurry and the dispersion medium are filled in a sealable container so that the total volume of the slurry and the dispersion medium is the same as the volume in the container, and the slurry is stirred together with the dispersion medium in a sealed state. Then, the spherical magnetic particles are deformed and fused to form a flat magnetic powder.

  The dispersion medium must be harder than spherical magnetic particles, for example, metal spheres such as aluminum, steel (steel), stainless steel, and lead, and metal oxides such as alumina, zirconia, silicon dioxide, and titania. Spherical sintered body made of an inorganic oxide such as silicon nitride, spherical sintered body made of inorganic nitride such as silicon nitride, spherical sintered body made of inorganic carbide such as silicon carbide, soda glass, lead glass, high specific gravity glass, etc. In particular, zirconia, steel (steel), stainless steel and the like having a specific gravity of 6 or more are preferable from the viewpoint of efficiency.

  The mechanical stress is applied to the spherical magnetic particles because the spherical magnetic particles are sandwiched between the dispersion medium and the dispersion medium or between the dispersion medium and the inner wall of the closed container when the dispersion medium collides. It is done by the shock given. Therefore, as the number of collisions between the dispersion media or between the dispersion media and the container wall increases, the deformation and fusion properties between the spherical magnetic particles improve.

Thus, the smaller the average particle size of the dispersion medium, the more the number existing per unit volume, the greater the number of collisions, and the better the deformation and fusion properties. If it is too small, it will be difficult to separate the dispersion medium from the slurry. Therefore, the average particle size of the dispersion medium needs to be at least 0.03 mm or more, preferably 0.04 mm or more.
In addition, when the average particle size of the dispersion medium is too large, the number of collisions decreases, so that the deformation and fusion property between the spherical magnetic particles deteriorates. Therefore, the upper limit of the average particle diameter of the dispersion medium is 3.0 mm.

As the container that can be sealed, a sealed container that rotates the uniaxial rotating body such as a disk, a screw, a blade, and a pin at a high speed together with the slurry by rotating at high speed is preferable.
Since this hermetic container is a simple uniaxial rotation system, it is easy to increase the size and is advantageous for industrial production.
Note that the above-described sealable container may be provided with an inlet and an outlet for introducing and discharging the slurry into and from the container, and the slurry may be circulated in the sealed container. In this case, the dispersion medium is previously stored in a sealed container, and a slurry in which spherical magnetic particles, a surfactant, and a solvent are mixed is introduced from the inlet and filled so that there is no space in the container. The slurry discharged from the outlet may be charged again into the sealed container.

Here, the filling amount of the slurry and the dispersion medium into the above-mentioned closed container is the same as the volume in the closed container. In other words, the slurry and the dispersion medium are filled in the sealed container without gaps.
Here, the reason why the slurry and the dispersion medium are filled in the sealed container without any gap is as follows.

FIG. 1 is a diagram showing a state in which a slurry 3 containing a spherical magnetic particle 2 and a dispersion medium 4 placed in an open container 1 having an open top are stirred at a high speed by being rotated at a high speed by a uniaxial rotating body 5. is there.
In this figure, when the uniaxial rotating body 5 rotates at a high speed, the liquid surface of the slurry 3 and the dispersion medium 4 becomes a mortar shape having a low vicinity of the central axis and a high peripheral edge due to centrifugal force.
The mechanical stress applied to the slurry 3 containing the spherical magnetic particles 2 and the dispersion medium 4 by the uniaxial rotating body 5 escapes into the mortar-like space, so that the entire inside of the open container 1 passes through the dispersion medium 4. The mechanical stress propagated to the spherical magnetic particles 2 becomes non-uniform, which causes a variation in the thickness of the obtained flat magnetic powder.

  In addition, the magnetic powder that is flat near the bottom of the mortar-shaped space (near the central axis) is discharged into the mortar-shaped space together with the dispersion medium and is subject to irregular impacts. May occur. Such variations in thickness, cracks and chipping of the magnetic powder are factors that increase the loss tangent in the VHF band. In addition, the real part μr ′ of the complex permeability is a factor that fluctuates in a frequency band from 70 MHz to 500 MHz.

FIG. 2 is a view showing that the slurry 3 and the dispersion medium 4 containing the spherical magnetic particles 2 charged in the sealed container 11 are stirred at a high speed by being rotated at a high speed by the uniaxial rotating body 5.
In this figure, even when the uniaxial rotating body 5 rotates at a high speed, the inside of the sealed container 11 is filled with the slurry 3 and the dispersion medium 4 containing the spherical magnetic particles 2, and as seen in the open container 1. There is no risk of creating a mortar-shaped space. Therefore, the mechanical stress applied to the slurry 3 containing the spherical magnetic particles 2 and the dispersion medium 4 by the uniaxial rotating body 5 is uniformly applied to the spherical magnetic particles 2 through the dispersion medium 4 in the entire sealed container 11. There is no possibility that the thickness of the flat magnetic powder which is propagated and obtained will vary. Further, the flat magnetic powder is not subjected to irregular impacts, and there is no possibility of cracking or chipping.

The rotational speed of the uniaxial rotating body 5 is determined by the size of the sealed container 11. For example, in the case of the sealed container 11 having an inner diameter of 120 mm, the slurry 3 containing the spherical magnetic particles 2 and the dispersion medium 4 are uniaxial so that the flow velocity near the radial outer peripheral end 5a of the uniaxial rotating body 5 is 5 m / second or more. It is preferable to set the rotation speed of the rotator 5, and it is more preferable to set the rotation speed of the uniaxial rotator 5 so that the flow velocity in the vicinity of the outer peripheral end 5a is 8 m / sec or more.
On the other hand, if the flow velocity in the vicinity of the outer peripheral edge 5a exceeds 15 m / s, there is a risk of destroying the flattened particles because the energy is too large, so the flow velocity in the vicinity of the outer peripheral edge 5a is 15 m / s or less. Preferably there is.

  In addition, when the internal volume of the airtight container 11 is small, there exists a possibility that the spherical magnetic particle 2 may remain in the obtained flat magnetic powder. The remaining spherical magnetic particles 2 increase the magnetic loss due to contact between the spherical magnetic particles 2 or contact between the spherical magnetic particles 2 and the flat magnetic powder. There is a risk of disturbing the orientation. Therefore, the flat magnetic powder is preferably 90% by mass or more of the total amount of the magnetic powder, more preferably 95% by mass or more, and further preferably 99% by mass or more. It is desirable not to include.

  Here, the reason why the spherical magnetic particles 2 remain when the inner volume of the sealed container 11 is small is that the mechanical stress such as the corner of the sealed container 11 and the joint between the rotating body 5 and the sealed container 11 is not sufficiently transmitted. This is probably because the dead space becomes relatively large. Therefore, when the internal volume of the sealed container 11 is increased, the dead space is relatively reduced, and therefore, the mechanical stress is sufficiently transmitted to the spherical particles 2, and the deformation and fusion property between the spherical magnetic particles is improved. As a result, the residual spherical magnetic particles 2 are reduced, and the substantially spherical magnetic particles 2 are eliminated.

Thus, the volume of the sealed container 11 in which substantially spherical magnetic particles 2 do not remain is preferably 1 L or more, more preferably 5 L or more.
As described above, the spherical magnetic particles are deformed and fused by the mechanical stress applied by the uniaxial rotating body 5 to form a flat magnetic powder.
Next, the flat magnetic powder is separated from the dispersion medium and the solvent. However, in the case where a solvent in which a resin described later is soluble is used, it may not be separated.

  The separation method is not particularly limited as long as the solvent can be removed from the slurry 3 after producing the flat magnetic powder, and examples thereof include heat drying, vacuum drying, freeze drying, and the like. And vacuum drying is preferred. In order to increase the drying efficiency, some solvent may be removed by a method such as solid-liquid separation before the drying step. As a solid-liquid separation method, a normal method such as a filtration operation such as a filter press or suction filtration, or a centrifugal separation operation using a decanter or a centrifuge may be used.

  The flat magnetic powder from which the solvent has been removed may be heat-treated at 50 ° C. or more and 200 ° C. or less for 1 hour or more and several hours or less. By this heat treatment, an oxide film can be formed on the surface of the magnetic powder, and an insulating flat magnetic powder can be obtained.

(Second step)
The above-mentioned flat magnetic powder is dispersed and mixed in a solution dissolved in an insulating material to form a mixture, and this mixture is used as a molding material.
The insulating material is as described above, but among the above insulating materials, it is preferable to use a liquid insulating material. When other insulating materials are used, the insulating material can be dissolved in a solvent to be a liquid. preferable.

When a thermosetting resin is used as the insulating material, the type and amount of the curing agent may be appropriately adjusted according to the type and amount of the thermosetting resin to be used.
In the case of using an epoxy resin as the thermosetting resin, a tertiary amine is preferable in that the condensation reaction between the epoxy groups is promoted to prevent generation of pores due to poor curing in the molded body of the composite magnetic body.

Examples of the tertiary amine include 1-isobutyl-2-methylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and the like. It is done.
In consideration of the point of promoting the condensation reaction of the functional group, the addition amount of the curing agent may be 0.5% by mass or more and 3% by mass or less with respect to the total mass of the thermosetting resin.
In addition, when using a thermoplastic resin as an insulating material, a hardening | curing agent is unnecessary.

In order to dissolve the above insulating material or adjust the viscosity, a solvent may be mixed as appropriate.
As the solvent, those capable of dissolving the above insulating material are preferable. For example, alcohols such as methanol, ethanol, 2-propanol, butanol, octanol, ethyl acetate, butyl acetate, ethyl lactate, propylene glycol monomethyl ether acetate , Propylene glycol monoethyl ether acetate, esters such as γ-butyrolactone, diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monomethyl ether, Ethers such as diethylene glycol monoethyl ether, acetone, methyl ethyl ketone, methyl isobutyl keto , Ketones such as acetylacetone and cyclohexanone, aromatic hydrocarbons such as benzene, toluene, xylene and ethylbenzene, and amides such as dimethylformamide, N, N-dimethylacetoacetamide and N-methylpyrrolidone are preferably used. A solvent may be used individually by 1 type and may be used in mixture of 2 or more types.
In order to improve the dispersibility of the magnetic powder in the molding material, it is also preferable to add a surfactant.

The solvent is preferably mixed in the mixture of the insulating material and the magnetic powder so as to be 30% by mass or more, and more preferably 35% by mass or more.
By mixing the solvent in an amount of 30% by mass or more, the viscosity of the obtained mixture is lowered. Therefore, even when the magnetic powders are aggregated during mixing, the aggregation is loosened and the dispersibility in the insulating material is improved. . Thereby, the porosity of a composite magnetic body can be reduced.
In addition, when there is too much quantity of a solvent, since it takes time for drying mentioned later and a void | hole may produce | generate at the time of drying, the quantity of a solvent is 50 mass% with respect to the total mass of magnetic powder and an insulating material. The following is preferable.

When a thermosetting resin is used as the insulating material, the content of the magnetic powder in the mixture is 10% by volume or more and 60% by volume or less in the total volume of the thermosetting resin, the curing agent, and the magnetic powder. More preferably, they are 30 volume% or more and 50 volume% or less.
Here, if the content of the magnetic powder is less than 10% by volume, it is not preferable because the magnetic powder is too small and the magnetic properties as a composite magnetic material are deteriorated. On the other hand, when the content of the magnetic powder exceeds 60% by volume, the magnetic powder is too much, and the fluidity of the mixture containing the magnetic powder, the thermosetting resin, the curing agent, and the solvent decreases. Therefore, since the moldability at the time of shape | molding using this mixture will fall, it is not preferable.
The composite magnetic body preferably does not contain spherical magnetic particles.

When a thermoplastic resin is used as the insulating material, the content of the magnetic powder in the mixture is preferably 10% by volume or more and 80% by volume or less in the total volume of the thermoplastic resin and the magnetic powder, more preferably 30 volume% or more and 60 volume% or less.
Here, if the content of the magnetic powder is less than 10% by volume, it is not preferable because the magnetic powder is too small and the magnetic properties as a composite magnetic material are deteriorated. On the other hand, when the content of the magnetic powder exceeds 80% by volume, the magnetic powder is too much, and the fluidity of the mixture containing the magnetic powder, the thermoplastic resin, and the solvent is lowered. Since the moldability at the time of shape | molding using a mixture will fall, it is not preferable.
The composite magnetic body preferably does not contain spherical magnetic particles.

The viscosity of the mixture is preferably 0.1 Pa · s or more and 10 ⁶ Pa · s or less, more preferably 0.3 Pa · s or more and 10 ⁴ Pa · s or less.
Here, when the viscosity is less than 0.1 Pa · s, it is not preferable because the fluidity becomes too high and the productivity in the drying process is deteriorated. On the other hand, when the viscosity exceeds 10 ⁶ Pa · s, the viscosity Is too high to cause orientation of the magnetic powder, and as a result, the orientation of the magnetic powder in the composite magnetic material is lowered, which is not preferable.

The mixing method is not particularly limited, and it is sufficient that the magnetic powder, the insulating material, the solvent, and the like are uniformly mixed or dispersed using a mixing device or the like.
The mixing device is not particularly limited as long as the magnetic powder, insulating material, solvent, and the like can be uniformly mixed or dispersed to form a slurry-like mixture. For example, a stirrer, a roll mill, a self-revolving type, etc. Examples include a mixer, a homogenizer, an ultrasonic homogenizer, a planetary mill, a sand mill, and a ball mill. When mixing with these apparatuses, the mixing conditions may be adjusted as appropriate so that the magnetic powder does not aggregate too much and is uniformly mixed or dispersed in the insulating material.

Moreover, when using a thermosetting resin or a thermoplastic resin as an insulating material, it is preferable to mix or disperse by heat kneading.
As a heat-kneading method, for example, a kneaded material mixed and dispersed by a pressure kneader, a biaxial kneader, a blast mill or the like can be produced.

(Third step)
The above molding material is molded or coated on a substrate, dried, heat-treated or fired.
As the molding method, a known molding method, for example, an extrusion method, a bar coating method, a pressing method, a doctor blade method, an injection molding method or the like is suitable. A dry film can be produced by forming a sheet or film of any shape using this forming method.
When the composite magnetic body is a laminate, it is preferably formed into a sheet or film by the doctor blade method.

When a thermosetting resin or a thermoplastic resin is used as the insulating material, a molded body can be produced by, for example, hot press molding, extrusion molding, injection molding, or the like. Among these methods, in order to improve the orientation of the magnetic powder in the insulating material, hot press molding that is stretched flat is preferable. In order to adjust the viscosity at the time of stretching, it is also preferable to add a plasticizer or perform surface treatment of the magnetic powder.
When the composite magnetic body is a laminated body, it is preferable to laminate or laminate those formed into a sheet shape or a film shape by a bar coating method or a doctor blade method.

  When it is necessary to adjust the viscosity, the molding material is molded after the solvent is volatilized and concentrated. If necessary, after applying the molding material on the base material, an orientation treatment for orienting the flat magnetic powder in a direction parallel to the sheet or film by orientation of the magnetic field may be performed before drying.

The method for orienting the magnetic powder in the molded body is not particularly limited as long as a magnetic field is applied so that the magnetic powder in the molded body can be oriented in one direction.
When a magnetic field is applied to the magnetic powder in the molded body, the magnetic powder cannot be oriented in one direction if the magnetic field lines are bent in the molded body. Therefore, it is preferable to apply the magnetic field so that the generated magnetic field lines are substantially parallel to the surface of the molded body.

  The magnitude of the magnetic field to be applied is preferably 100 gauss or more and 3000 gauss or less. If the magnitude of the magnetic field is less than 100 gauss, the magnetic field is too small, and the magnetic powder in the compact may not be sufficiently oriented in one direction. On the other hand, if it exceeds 3000 gauss, the magnetic field becomes too large, and there is a risk that the magnetic powder will be agglomerated and separated from the resin, which is an insulating material, by this magnetic field. This is not preferable because non-uniformity may occur.

  Examples of the orientation method in the case of using a thermosetting resin or a thermoplastic resin as the insulating material include a method of orienting tabular magnetic particles by the orientation of the magnetic field as described above while maintaining the fluidity by heating. It is done.

As the heat treatment or firing conditions, heat treatment in a reducing atmosphere or vacuum, or pressure heat treatment by hot pressing or the like is preferably used.
By heat treatment or baking, the thermosetting resin is hardened or densified by softening the thermoplastic resin. Therefore, the porosity of the molded body during heat treatment or firing is preferably 20% or less.

When a resin is used as the insulating material when applying pressure to the molded body with a press apparatus, it is preferable to apply pressure at a temperature higher than the softening temperature of the resin and lower than the curing start temperature in order to effectively reduce pores. In particular, when a thermoplastic resin is used, it is necessary to apply pressure at a temperature equal to or higher than the softening temperature of the resin to fuse the resins together.
The pressure during pressing may be adjusted as appropriate, but it is preferable to apply a pressure of about 5 MPa to 20 MPa.
The composite magnetic body of this embodiment is obtained by the above.

[antenna]
The antenna of this embodiment is an antenna that loads the above-described composite magnetic material and transmits, receives, or transmits / receives electromagnetic waves in a frequency band from 70 MHz to 500 MHz.
The shape of the antenna can be appropriately changed according to the size and shape of the loaded communication device, and examples thereof include a spiral shape and a meandering shape.

The method for loading the antenna with the composite magnetic body is not particularly limited, and the conductor such as a copper wire constituting the antenna (hereinafter referred to as “antenna conductor”) is covered with the composite magnetic body. What is necessary is just to load by a well-known method.
Here, “loading” refers to bringing the composite magnetic material into contact with or close to the antenna conductor in order to obtain an effect such as wavelength reduction by electromagnetic interaction.

The type and shape of the antenna are not particularly limited, and a monopole antenna, a loop antenna, a helical antenna, a patch antenna, an F-type antenna, an L-type antenna, or the like is preferably used. Further, a matching circuit may be used in combination in order to reduce the size of the antenna.
For example, a monopole antenna or an L-shaped antenna can be obtained by sandwiching the above composite magnetic body into a rod-like or long plate-like shape around the antenna conductor.
The helical antenna can be obtained by winding a long and extremely thin antenna conductor made of copper wire or the like in a coil shape around a rod-shaped composite magnetic material obtained by processing the above-described composite magnetic material into a rod shape.
With these antennas, it is possible to obtain a small antenna having a length shorter than ¼ of the desired wavelength due to the wavelength shortening effect.

FIG. 3 is a schematic diagram showing a method of feeding a monopole antenna, which is an example of the antenna of the present embodiment. The monopole antenna 21 has a rod-shaped antenna conductor 22 and a surface of the antenna conductor 22 embedded by embedding the antenna conductor 22. And a plate-like composite magnetic body 23 coated with
The monopole antenna 21 is connected to a ground plane 24 made of a conductor having a predetermined shape via a coaxial connector or the like, and an AC signal transmitter 26 is connected to a connection portion 25 that is an inner conductor of the coaxial connector or the like as a feeding point. It is connected. The connecting portion 25 and the ground plane 24 serving as a feeding point are electrically insulated.
In the same manner as described above, the antenna is connected to the ground plane 24 via a connector or the like, and the AC signal transmitter 26 is connected so that the connection portion 25 serves as a feeding point.

[Communication device]
The communication device of this embodiment includes the antenna described above.
The communication device is not particularly limited as long as it is a device that transmits, receives, or transmits / receives various information via electromagnetic waves. For example, personal computers, portable telephones, portable information terminals, multifunctional portable information terminals such as smartphones, communication devices such as PDAs (Personal Digital Assistants), various electronic devices such as audio devices, video devices, camera devices, etc. It is done.
In these communication devices, the antenna may be provided outside the communication device, or may be built in either.

Here, taking a portable telephone as an example of the communication device, various methods of attaching the antenna will be described.
FIG. 4 is a perspective view showing an example of a kind of mobile phone of the communication apparatus of the present embodiment. The mobile phone 31 has a display function including a liquid crystal display, an organic EL display, or the like on the front surface of the housing 32. The display unit 33 is provided, and a ground plate (not shown) is provided on the back side of the display unit 33, and a copper wire or the like disposed in the rod-shaped monopole antenna 34 via a connector or the like on the ground plate. An antenna conductor 35 made of a conductor is connected, and an electronic circuit (not shown) of the portable telephone 31 is connected through this connection portion. The antenna conductor 35 of the monopole antenna 34 is covered with a composite magnetic material 36.

The monopole antenna 34 is removable from the housing 32 and can be housed in the housing 32. During communication, the monopole antenna 34 is pulled out from the housing 32 as necessary to perform communication. When not communicating, the housing 32 is provided. It is designed to be pushed into the storage.
The monopole antenna 34 does not have to be rod-shaped and may be extendable / contractable.
The monopole antenna 34 is preferably provided at a position that does not overlap the display unit 33 or the like in consideration of improving the antenna gain. In the case where the monopole antenna 34 is provided at a position overlapping with the display unit 33 and the like, it is preferable that the monopole antenna 34 and the display unit 33 are spaced from each other.

FIG. 5 is a perspective view showing another example of a kind of mobile phone of the communication apparatus of the present embodiment. The mobile phone 41 is a display comprising a liquid crystal display, an organic EL display, or the like on the front surface of the housing 42. A display portion 43 having a function is provided, and an external antenna terminal 44 is provided on the side surface. A connection terminal 46 provided on the side surface of the rod-shaped monopole antenna 45 is fitted into the external antenna terminal 44. The monopole antenna 45 is connected to a ground plate (not shown) provided on the back side of the display unit 43 via a connection terminal 46 and an external antenna terminal 44, and the electronic phone of the portable telephone 41 is connected via this connection unit. A circuit (not shown) is connected. In this monopole antenna 45, an antenna conductor 47 made of a conductor such as a copper wire is covered with a composite magnetic body 48.
This portable telephone 41 can be attached and detached by inserting / removing the connection terminal 46 of the monopole antenna 45 to / from the external antenna terminal 44.

  FIG. 6 is a partial perspective view showing a part of still another example of a kind of mobile phone of the communication apparatus according to the present embodiment. The mobile phone 51 includes a liquid crystal display or an organic EL on the front surface of the casing 52. A ground plane 53 is provided on the back side of a display unit (not shown) having a display function such as a display, and an L-shaped antenna 54 is provided at a position that does not overlap the ground plane 53 (in FIG. 6, above the ground plane 53). An antenna conductor 55 made of a conductor such as a copper wire disposed in the L-shaped antenna 54 is connected to the ground plane 53 via a connector or the like, and an electronic circuit (not shown) of the portable telephone 51 is connected via this connection portion. Is connected. The L-shaped antenna 54 has an antenna conductor 55 covered with a composite magnetic body 56.

  FIG. 7 is a partial perspective view showing a part of still another example of a kind of mobile phone of the communication apparatus according to the present embodiment. The mobile phone 61 includes a liquid crystal display or an organic EL on the front surface of the housing 62. A ground plate 63 is provided on the back side of a display unit (not shown) having a display function such as a display, and a helical antenna 64 is provided at a position that does not overlap the ground plate 63 (above the ground plate 63 in FIG. 7). A helical antenna conductor 66 wound around a rod-shaped composite magnetic body 65 of the helical antenna 64 is connected to the ground plate 63 via a connector or the like, and an electronic circuit (not shown) of the portable telephone 61 is connected via this connection portion. ) Is connected.

  According to each of the above examples, since the mounted monopole antennas 34 and 45, the L-shaped antenna 54 or the helical antenna 64 are both small, the antenna can be arranged in a narrow space in the portable telephone, A portable telephone with a high antenna gain can be obtained without electromagnetic waves being blocked by components other than the antenna.

According to the composite magnetic body of this embodiment, the magnetic powder is flattened, and the real part μr ′ of the complex permeability in the frequency band from 70 MHz to 500 MHz is 7 or more, and the loss tangent tan δμ of the complex permeability is Since it is 0.05 or less, there is almost no frequency dependency of μr ′, and the wavelength shortening rate in this frequency band can be increased.
Therefore, if this composite magnetic body is applied to an antenna such as a VHF band, it is possible to prevent the generation of eddy currents on the surface of the composite magnetic body, to prevent the decrease in μr ′, and to further reduce the size of the antenna. Can be achieved.
Furthermore, if this composite magnetic body is applied to an electronic component having an antenna such as a VHF band, the antenna and the electronic component can be further reduced in size.

  In particular, if tan δμ of the composite magnetic material is 0.1 or less in the frequency band from 70 MHz to 500 MHz, preferably from 90 MHz to 220 MHz, the magnetic loss can be reduced and the gain of the antenna can be improved. Therefore, by applying this composite magnetic body to an antenna such as a VHF band or an electronic component, a small antenna having a high gain can be obtained.

If the porosity of this composite magnetic body is 20% or less, power loss due to impedance matching can be suppressed.
Further, if the real part εr ′ of the complex dielectric constant in the frequency band from 70 MHz to 500 MHz of the composite magnetic material is 15 or more and the loss tangent tan δε of the complex dielectric constant is 0.1 or less, the antenna can be reduced in size and gain. Can be improved.
Therefore, if this composite magnetic material is applied to an antenna or electronic component in a frequency band (VHF band or the like) from 70 MHz to 500 MHz, an antenna having a small size and a high gain can be obtained.

  According to the method for producing a composite magnetic body of the present embodiment, a slurry obtained by dispersing spherical magnetic particles having an average particle diameter of 3 μm or less in a solution and a dispersion medium are placed in a sealable container, the slurry and the The total volume of the dispersion medium is filled so as to be the same as the volume in the container, and this slurry is stirred together with the dispersion medium in a sealed state, and the spherical magnetic particles are deformed and fused together to form a flat shape. A first step of making the magnetic powder, a second step of mixing the flat magnetic powder with an insulating material to form a molding material, and molding or applying the molding material on a substrate, And a third step of drying, heat treatment or firing, so that it is possible to easily produce a composite magnetic body having μr ′ of 7 or more and tan δμ of 0.1 or less in a frequency band from 70 MHz to 500 MHz. it can.

  According to the antenna of this embodiment, since the composite magnetic body of this embodiment is loaded and electromagnetic waves in the frequency band from 70 MHz to 500 MHz are transmitted, received, or transmitted / received, further miniaturization of the antenna is achieved. be able to.

  According to the communication apparatus of the present embodiment, since the small antenna of the present embodiment is provided, the degree of freedom of placing the antenna in a place that is not easily affected by other electronic devices that block electromagnetic waves is high, and good transmission and reception are possible. A possible small communication device can be obtained.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.

[Example 1]
200 g of magnetic particles having an average particle diameter of 0.25 μm composed of 4% by mass of zinc, 76% by mass of nickel, and 20% by mass of iron were dissolved as a surfactant into a nitrogen-containing graft polymer Floren KDG-2400 (manufactured by Kyoeisha Chemical Co., Ltd.). A slurry was prepared by mixing with 400 g of xylene and 400 g of isopropyl alcohol.
Next, a sand mill Ultra Apex Mill UAM-5 (manufactured by Kotobuki Kogyo Co., Ltd.) having a circulation volume of 5 L and having a container volume of 5 L as shown in FIG. Zirconia beads were charged, and then the above slurry was charged to fill the sealed container. Here, piping was made so that the slurry discharged from the sealed container was charged again and circulated.

In this state, until the residence time of the slurry in the airtight container reached 20 minutes, stirring was performed at a rotational speed at which the flow velocity near the outer peripheral end of the rotating body was 10 m / second to produce a flat magnetic powder.
Next, after drying the obtained flat magnetic powder to dissipate the solvent, a predetermined amount of this flat magnetic powder (40% by volume with respect to the total amount of resin and magnetic powder) Epoxy resin EPICLON HP-7200L (manufactured by DIC Corporation) was added to a resin varnish obtained by diluting with xylene to a solid content ratio of 40% and stirred and mixed.

The obtained mixture was formed into a 30 mm square and 100 μm thick square film by the doctor blade method.
Next, this film was dried at 90 ° C. in the air for 1 hour to form a dry film, and then press fired in a reduced pressure press. The press conditions were as follows: normal pressure was raised to 130 ° C. in 20 minutes, then 2 MPa pressure was applied and held for 5 minutes, then heated to 160 ° C. and held for 40 minutes to cure the resin, 30 mm square A composite magnetic body of Example 1 in the form of a square film having a thickness of 50 μm was obtained.

Next, the electromagnetic characteristics and porosity of the composite magnetic material were evaluated by the following methods.
(1) Electromagnetic characteristics The complex magnetic material real part μr ′, complex dielectric constant real part εr ′, complex magnetic permeability tan δμ and complex dielectric constant tan δε are represented by a material analyzer E4991A type (manufactured by Agilent Technologies). And measured at room temperature (25 ° C.) in the atmosphere.

(2) Porosity The dimensions and mass of the composite magnetic material were measured, and the actual density was calculated based on these measured values.
On the other hand, the theoretical density (≈measured density) of the resin was calculated from these measured values by measuring the dimensions and mass of the cured body of resin alone. The theoretical density of the magnetic powder was the X-ray theoretical density determined from the X-ray diffraction pattern of the magnetic powder.
These values were substituted into the above equation (4) to calculate the porosity of the composite magnetic material.

  As a result, the porosity of the composite magnetic material of Example 1 was 13.1%. The real part μr ′ of the complex permeability at 90 MHz was 12, and the loss tangent tan δμ was 0.02, the real part μr ′ of the complex permeability at 220 MHz was 13, and the loss tangent tan δμ was 0.03.

Further, when the shape of the magnetic particles in the composite magnetic material was observed with a scanning electron microscope (SEM), the average thickness of 50 flat magnetic powders was 0.08 μm, and the average major axis was 0.5 μm. Yes, the average aspect ratio was 6.25. In addition, spherical magnetic particles, magnetic powder having a thickness of 0.01 μm or more and 0.5 μm or less, a major axis of 0.05 μm or more and 20 μm or less, and an aspect ratio of 5 or more are not observed, and spherical magnetic particles are not I was not able to admit.
FIG. 8 shows μr ′, μr ″, and tan δμ of the composite magnetic material, and FIG. 9 shows a scanning electron microscope (SEM) image of the composite magnetic material.

[Example 2]
200 g of magnetic particles having an average particle diameter of 0.2 μm composed of 78% by mass of nickel and 22% by mass of iron are mixed with 800 g of xylene in which nitrogen-containing graft polymer Floren KDG-2400 (manufactured by Kyoeisha Chemical Co., Ltd.) is dissolved as a surfactant. A slurry was prepared.
Next, a sand mill Ultra Apex Mill UAM-5 (manufactured by Kotobuki Kogyo Co., Ltd.) having a circulation volume of 5 L and a container volume of 5 L as shown in FIG. Zirconia beads were charged, and then the above slurry was charged to fill the sealed container. Here, circulation was not performed, and the inlet of the sealed container was liquid-sealed.

In this state, magnetic powder was produced by stirring for 4 hours at a rotational speed at which the flow velocity near the outer peripheral edge of the rotating body in the sealed container was 10 m / sec.
Next, after drying the obtained magnetic powder to dissipate the solvent, a predetermined amount of this magnetic powder (40% by volume with respect to the total volume of the resin and the magnetic powder) was used as a polystyrene resin dick styrene MH6800. -1 (manufactured by DIC Corporation) was added to a resin varnish diluted with toluene to a solid content ratio of 40% and mixed with stirring.

Next, the mixture was formed into a sheet on a polyethylene terephthalate (PET) film so as to have a thickness of 0.1 mm using a bar coater.
After forming the sheet, a 900 gauss magnetic field was applied to the surface of the sheet in the horizontal direction for 6 minutes. Subsequently, it was air-dried by applying hot air of 80 ° C. Next, a composite magnetic body of Example 2 was obtained by applying a press pressure of 10 MPa at 95 ° C. for 5 minutes.

When the composite magnetic body of Example 2 was evaluated in the same manner as in Example 1, the porosity of the composite magnetic body was 13%.
Further, μr ′ at 90 MHz was 9 and tan δμ was 0.02, μr ′ at 220 MHz was 9 and tan δμ was 0.02.

The shape of the magnetic particles in the composite magnetic material was observed in the same manner as in Example 1. As a result, the average thickness of 50 magnetic particles was 0.15 μm, the average major axis was 1.2 μm, and the average aspect ratio was 8 Met. In addition, spherical magnetic particles, magnetic powder having a thickness of 0.01 μm or more and 0.5 μm or less, a major axis of 0.05 μm or more and 20 μm or less, and an aspect ratio of 5 or more are not observed, and spherical magnetic particles are not I was not able to admit.
FIG. 10 shows μr ′, μr ″, and tan δμ of this composite magnetic material.

"Example 3"
Instead of using magnetic particles having an average particle diameter of 0.2 μm consisting of 78 mass% of nickel and 22 mass% of iron and having an average particle diameter of 0.2 μm, using magnetic particles having an average particle diameter of 0.2 μm consisting of 88 mass% of nickel and 12 mass% of iron The composite magnetic body of Example 3 was obtained in the same manner as Example 2.

When the obtained composite magnetic body was evaluated in the same manner as in Example 1, the porosity of the composite magnetic body was 12%.
The real part μr ′ of the complex permeability at 90 MHz was 9 and the loss tangent tan δμ was 0.03, the real part μr ′ of the complex permeability at 220 MHz was 9.5 and the loss tangent tan δμ was 0.04. .

  Further, when the shape of the magnetic particles in this composite magnetic material was observed in the same manner as in Example 1, the average thickness of 50 magnetic powders was 0.18 μm, the average major axis was 1.2 μm, and the average aspect ratio was It was 6.7. In addition, spherical magnetic particles, magnetic powder having a thickness of 0.01 μm or more and 0.5 μm or less, a major axis of 0.05 μm or more and 20 μm or less, and an aspect ratio of 5 or more are not observed, and spherical magnetic particles are not I was not able to admit.

Example 4
Instead of magnetic particles having an average particle diameter of 0.2 μm consisting of 78 mass% of nickel and 22 mass% of iron, magnetic particles having an average particle diameter of 0.2 μm consisting of 68 mass% of nickel and 32 mass% of iron were used. The composite magnetic body of Example 4 was obtained in the same manner as Example 2.

When the obtained composite magnetic body was evaluated in the same manner as in Example 1, the porosity of the composite magnetic body was 12%.
The real part μr ′ of the complex permeability at 90 MHz is 9.5 and the loss tangent tan δμ is 0.03, and the real part μr ′ of the complex permeability at 220 MHz is 9.8 and the loss tangent tan δμ is 0.04. there were.

  Further, when the shape of the magnetic particles in this composite magnetic material was observed in the same manner as in Example 1, the average thickness of 50 magnetic powders was 0.2 μm, the average major axis was 1.2 μm, and the average aspect ratio was 6. In addition, spherical magnetic particles, magnetic powder having a thickness of 0.01 μm or more and 0.5 μm or less, a major axis of 0.05 μm or more and 20 μm or less, and an aspect ratio of 5 or more are not observed, and spherical magnetic particles are not I was not able to admit.

"Example 5"
Example 2 was used in the same manner as in Example 2 except that a resin in which a polystyrene resin and a styrene / butadiene-based thermoplastic elastomer Toughprene 126S (manufactured by Asahi Kasei Chemicals Corporation) were mixed at a mass ratio of 50:50 was used instead of the polystyrene resin. Thus, a composite magnetic body of Example 5 was obtained.

When the obtained composite magnetic body was evaluated in the same manner as in Example 1, the porosity of the composite magnetic body was 10.5%.
The real part μr ′ of the complex permeability at 90 MHz was 12 and the loss tangent tan δμ was 0.02, the real part μr ′ of the complex permeability at 220 MHz was 12, and the loss tangent tan δμ was 0.02.

  Further, when the shape of the magnetic particles in the composite magnetic material was observed in the same manner as in Example 1, the average thickness of 50 magnetic powders was 0.15 μm, the average major axis was 1.2 μm, and the average aspect ratio was It was 8. In addition, spherical magnetic particles, magnetic powder having a thickness of 0.01 μm or more and 0.5 μm or less, a major axis of 0.05 μm or more and 20 μm or less, and an aspect ratio of 5 or more are not observed, and spherical magnetic particles are not I was not able to admit.

"Example 6"
Instead of mixing so that the polystyrene resin becomes 40% by volume, a resin in which a polystyrene resin and a styrene / butadiene-based thermoplastic elastomer Toughprene 126S (manufactured by Asahi Kasei Chemicals Co., Ltd.) are mixed at a mass ratio of 50:50 is used. A composite magnetic body of Example 6 was obtained in the same manner as in Example 2 except that the mixed resin was mixed so that the mixed resin was 60% by volume with respect to the total volume of the magnetic powder.

When the obtained composite magnetic body was evaluated in the same manner as in Example 1, the porosity of the composite magnetic body was 9.7%.
In addition, μr ′ at 90 MHz was 16 and tan δμ was 0.03, μr ′ at 220 MHz was 15.4, and tan δμ was 0.03.

  Further, when the shape of the magnetic particles in the composite magnetic material was observed in the same manner as in Example 1, the average thickness of 50 magnetic powders was 0.15 μm, the average major axis was 1.2 μm, and the average aspect ratio was It was 8. In addition, spherical magnetic particles, magnetic powder having a thickness of 0.01 μm or more and 0.5 μm or less, a major axis of 0.05 μm or more and 20 μm or less, and an aspect ratio of 5 or more are not observed, and spherical magnetic particles are not I was not able to admit.

"Comparative Example 1"
200 g of magnetic particles having an average particle diameter of 0.25 μm composed of 4% by mass of zinc, 76% by mass of nickel, and 20% by mass of iron were dissolved as a surfactant into a nitrogen-containing graft polymer Floren KDG-2400 (manufactured by Kyoeisha Chemical Co., Ltd.). A slurry was prepared by mixing with 400 g of xylene and 400 g of isopropyl alcohol.

  Next, an upper open-type sand mill as shown in FIG. 1 was used as an open container, and zirconia beads having an average particle diameter of 200 μm were charged as a dispersion medium into the vessel of the open container, and then the above slurry was charged. . Here, magnetic powder was produced by stirring for 30 minutes at a rotational speed at which the flow velocity near the outer peripheral edge of the rotating body in the vessel was 10 m / sec.

Using the obtained magnetic powder, a film-like composite magnetic material of Comparative Example 1 was obtained in the same manner as in Example 1.
When the obtained film-like composite magnetic material was evaluated in the same manner as in Example 1, the porosity of the composite magnetic material was 9.7%.
In addition, μr ′ at 90 MHz was 2.6 and tan δμ was 0.09, μr ′ at 220 MHz was 2.8, and tan δμ was 0.11.

Further, when the shape of the composite magnetic material was observed with a scanning electron microscope (SEM), the magnetic powders were irregularly overlapped with each other, and the thickness of 0.5 μm or more and spherical magnetic particles were also observed. It was done.
FIG. 11 shows the complex magnetic permeability (real part μr ′ and imaginary part μr ″) and loss tangent (tan δ) of the composite magnetic body, and FIG. 12 shows a scanning electron microscope (SEM) image of the composite magnetic body. Show.

"Example 7"
The mixture obtained in the same manner as in Example 1 was formed into a film by the doctor blade method. Next, this film was dried at 90 ° C. in the air for 1 hour to produce 12 dry films having a length of 250 mm, a width of 30 mm, and a thickness of 60 μm.

  Next, these dry films were laminated, and a copper wire having a diameter of 0.6 mm and a length of 250 mm was sandwiched between the sixth and seventh sheets as an antenna wire, and then press firing was performed using a vacuum press device. . The press conditions were as follows: normal pressure was raised to 130 ° C. in 20 minutes, then 2 MPa pressure was applied and held for 5 minutes, then heated to 160 ° C. and held for 40 minutes to cure the resin. A monopole antenna 21 in which an antenna conductor 22 made of a copper wire is sandwiched between composite magnetic bodies 23 made of a laminate of a dry film having a length of 250 mm, a width of 30 mm, and a thickness of 0.8 mm as shown in FIG.

Next, the monopole antenna 21 was connected to the center of a 500 mm square conductor ground plate 24, and 50 Ω was fed by the AC signal oscillator 26 using the connection point 25 as a feeding point.
Here, the resonance frequency of the monopole antenna 21 was measured, and for comparison, the resonance frequency of only a copper wire having a diameter of 0.6 mm and a length of 250 mm was measured.
As a result, the resonance frequency was 273 MHz only for the copper wire, whereas the monopole antenna of this example was 180 MHz, and the shortening rate converted to the wavelength was about 66%. From this result, it was found that the length of the 180 MHz antenna in the VHF band was reduced by about 34% by loading the composite magnetic material of this example.

DESCRIPTION OF SYMBOLS 1 Open container 2 Spherical magnetic particle 3 Slurry 4 Dispersion medium 5 Uniaxial rotating body 11 Sealed container 21 Monopole antenna 22 Antenna conductor 23 Composite magnetic body 24 Ground plate 25 Connection part 26 AC signal transmitter 31 Portable telephone 32 Case 33 Display unit 34 Monopole antenna 35 Antenna conductor 36 Composite magnetic body 41 Mobile phone 42 Housing 43 Display unit 44 External antenna terminal 45 Monopole antenna 46 Connection terminal 47 Antenna conductor 48 Composite magnetic body 51 Mobile phone 52 Housing 53 Ground plate 54 L-shaped antenna 55 Antenna conductor 56 Composite magnetic body 61 Portable telephone 62 Case 63 Ground plate 64 Helical antenna 65 Composite magnetic body 66 Antenna conductor

Claims (8)

In a composite magnetic body in which magnetic powder is dispersed in an insulating material,
The magnetic powder is flat,
The composite magnetic body, wherein the real part μr ′ of the complex permeability in the frequency band from 70 MHz to 500 MHz is 7 or more.   2. The composite magnetic body according to claim 1, wherein the loss tangent tan δμ of the complex permeability in the frequency band from 70 MHz to 220 MHz is 0.1 or less.   The composite magnetic body according to claim 1, wherein the porosity is 20% or less.   4. The real part εr ′ of the complex dielectric constant in the frequency band from 70 MHz to 500 MHz is 15 or more, and the loss tangent tan δε of the complex dielectric constant is 0.1 or less. The composite magnetic body described.   The average thickness of the magnetic powder is 0.01 µm or more and 10 µm or less, the average major axis is 0.05 µm or more and 20 µm or less, and the average aspect ratio (major axis / thickness) is 5 or more. 5. The composite magnetic material according to any one of 4 above. A slurry and a dispersion medium in which spherical magnetic particles having an average particle diameter of 3 μm or less are dispersed in a solution are placed in a sealable container, and the total volume of the slurry and the dispersion medium is the same as the volume in the container. A first step of stirring the slurry together with the dispersion medium in a sealed state, and deforming and fusing the spherical magnetic particles to form a flat magnetic powder;
A second step of mixing the flat magnetic powder with an insulating material to form a molding material;
A third step in which the molding material is molded or applied onto a substrate, dried, heat-treated or baked;
A method for producing a composite magnetic body comprising: Loading the composite magnetic body according to any one of claims 1 to 5,
An antenna characterized by transmitting, receiving, or transmitting / receiving electromagnetic waves in a frequency band from 70 MHz to 500 MHz.   A communication apparatus comprising the antenna according to claim 7.